Prior art air entrapment tunnel boats including catamarans, air entrapment tunnel monohulls, etc. are designed for the tunnel ceilings to become totally ventilated at design speeds and thereby reduce wetted surface drag while achieving some aerodynamic lift.
Other prior art watercraft, as for example, the Hickman Sea Sled, Boston Whalers, Tri-hulls and cathedral hulls are designed to keep aft portions of their entrapment tunnels at least partially immersed. The majority of these tunnels are rearwardly sloping and in cross section, typically arcuate. Tunnels that were angular were formed by the convergence of the main hull bottom deadrise and ama inboard side deadrise or main hull side deadrise above the chine and ama inboard side. Some tunnels had a distinct third ceiling surface that was usually of constant width in the aft section and were either flat horizontally or had very little deadrise.
Either submerged propellers or waterjets lose efficiency and effectiveness when ventilated and this has been a serious problem with prior art craft of the type described above. Since the tunnels of the craft constructed in accordance with the present invention are not formed by the convergence of the ama and main hull sides or bottom, the tunnel and main hull are treated as separate running bottoms designed to compliment each other to optimize total performance.